The present invention relates to an ink-jet recording device composed of a carriage reciprocated in the direction of the width of a recording medium, an ink-jet recording head provided to the carriage and ink supply means mounted on the carriage for supplying ink to the recording head, more detailedly relates to technique for supplying ink while maintaining negative pressure applied to the recording head.
An ink jet recording device used for printing a large number of pages is arranged, as disclosed in Japanese published examined patent application No. Hei4-43785 for example, such that an ink tank, e.g. a cassette, is installed in the body, and connected to an ink supply unit mounted on a carriage via an ink supply tube to supply ink to be consumed for printing to a recording head via the ink supply unit.
This arrangement makes it possible to significantly eliminate change of ink pressure associated with the extension or the bending of a tube during the movement of the carriage, thereby maintaining print.
In order to enhance color print quality, a recording device is available, which uses plural kinds of ink, i.e. ink of different optical densities, for the same type color. In such recording device, the number of ink tubes is increased as the kinds of ink are increased. Since each ink tube must be guided to follow the movement of the carriage, a structure for wiring each tube becomes complicated or restricted. Further, the elasticity and rigidity of the tube influences the movement of the carriage, hindering high-speed printing.
To solve such a problem, as disclosed in Japanese published unexamined patent application No. Hei10-244685, a recording device has been proposed, which includes an ink supply unit, mounted on a carriage, for supplying ink to an ink-jet recording head, an ink cartridge installed on the body side, and an ink supplementing unit which is connected by a conduit and detachably engaged with the ink supply unit.
With this arrangement, the carriage is moved during printing in a state that the ink supply unit is detached from the conduit such as a tube, and the ink supply unit is connected to the conduit only when the ink supply unit should be supplemented by ink. Therefore, the tube forming the conduit is not required to follow the movement of the carriage, and wiring can be simplified. The carriage can be moved at high speed because the tube is not extended or is not contracted following the movement of the carriage, and thus the high speed printing can be realized.
However, as the supply of ink from the ink cartridge installed on the body side to the ink supply unit depends upon slight negative pressure caused by expansion force of an elastic member preliminarily installed in the ink supply unit, the recording device suffers from a problem that the negative pressure decreases to reduce the filled quantity of ink and to consume increased time period for ink filling as air is accumulated in the ink supply unit in association with a large number of times the ink filling is repeated.
To solve this problem, as disclosed in Japanese published unexamined patent application Hei8-174860, a recording device has been proposed, in which a differential pressure valve mechanism is disposed between the ink storage chamber side of the ink supply unit and the recording head, the mechanism having a membrane opened or closed depending upon the differential pressure of ink.
This arrangement makes it possible to supply ink to the recording head while maintaining the negative pressure, but still suffers from a problem that as the membrane also fluctuates as ink fluctuates due to the movement of the carriage, the ink to be supplied to the recording head is difficult to finely maintain the negative pressure therein.
In addition, as the membrane is disposed to extend horizontally, increased area of the membrane, thus increased installation space therefor is required to open or close valve means with a slight difference of the negative pressure to be maintained to the recording head. Consequently, the carriage of the recording device using plural kinds of ink for printing is large in size.